The invention is directed to a dental handpiece which has a drive transmission including a first and second drive shaft section for transmitting rotational motion from a drive motor to an acceptance sleeve or chuck which rotatably supports a dental tool in the head housing of the handpiece. In order to obtain a different drive relation, the first drive shaft has a pair of coaxially arranged gears of different number of teeth and the second drive shaft can be mounted so a gear on its end will engage a selected one of the two gears to enable changing the drive ratio. In addition, the handpiece has cooling agent lines or segments with at least two line segments in the grip section being connected together by a rotatable coupling consisting of an annular channel or groove in one of the members cooperating with a radially extending port and the other member when the two members are telescopically assembled together with sealing rings adjacent the channels to enable rotation between the members which are held to be free of any axial displacement.
In known dental handpieces, the handle or grip section in the head part forms a so-called grip part or angle which can be rotated with respect to the drive part and can be releasably removed from the drive part. From this end, the drive end contains a guide shank or projection which surrounds the drive shaft. The guide shank or projection is engaged in a corresponding bore in the grip part until the gear of the drive shaft is engaged with a drive shaft section of the corresponding grip part. In this position, the handpiece is secured against axial slippage by means of a catch device which is operationally releasable and essentially consists of a snap ring groove in one of the parts and a catch spring carried by the other part and radially engaged in the ring groove to form the coupling or connection therebetween.
This type of coupling enables relative rotation between the drive part and the grip part or section and when cooling agent transmission lines are internally provided in the handpiece, the coupling must provide a rotational coupling for the two cooling line sections. Such a rotational coupling comprises a cooling line in one of the parts such as the motor part terminating in an angular groove on the projection and the grip part having radial ports extending into the cooling lines contained therein which radial ports are in communication with the annular groove when the two parts are assembled together. To insure sealing between the two parts, sealing members such as O-rings are provided adjacent the annular grooves.
In order for the handpiece to be operative at different speed ranges, a plurality of handpiece units consisting of head parts, neck parts and grip pieces are made available with each of these units having a different step down or respectively step up in the gear ratio. Thus, by selecting one of these handpiece units and assembling it on the drive part, a desired step up or step down in the gear ratio can be obtained.
The use of different and complete handpiece units as mentioned above to obtain different drive speeds for the tool involves a relatively large cost in terms of both structure and pieces. This is because each handpiece unit consists of a head part with a head housing, a neck and a handle or grip piece or part. Another disadvantage is that the rotatable coupling if provided between the handpiece units and the drive part will be released and uncoupled during each of the transfers or changes in the handpiece unit. Such constant coupling and uncoupling of the rotatable connection increases a danger of dust or dirt penetrating into the various cooling line sections such as the annular channel and/or radial ports. The constant coupling and uncoupling also applies shear stresses on each of the sealing rings. The repair or servicing of the cooling lines, which may become necessary due to blockage thereof, can generally only be carried out in a work shop. Then the entire handpiece unit is not available to the dentist during these times of repair.